1. Field of the Invention
The present invention relates to a method of producing a synthetic resin emulsion which can be suitably used in a variety of fields related to paints, adhesives, fibers, paper, civil engineering, etc.
As the synthetic resin emulsion produced by the method of the present invention contains an ultra high molecular weight polymer, films formed from the emulsion, moldings formed from the emulsion and processed products formed by using the films and/or moldings achieve high mechanical characteristics and chemical stability.
2. Discussion of the Background
A number of synthetic resin emulsions containing ultra high molecular polymers have been proposed.
For example, Japanese Patent Publication No. 1-53281 discloses a method of producing an ultra high molecular weight polymer, which method uses an emulsifier and a redox initiator containing 0.001-0.2 parts by weight of either a hydroperoxide or a persulfate per 100 parts by weight of a vinyl monomer having radical-polymerizing activity.
In many of the known methods of producing an ultra high molecular weight polymer emulsions disclosed so far including the above-mentioned method, oxygen in the atmosphere of the reaction system was substantially removed. However, reduction of oxygen concentration in the aqueous phase of the reaction system was not carefully considered in any of the known methods. For example, although some of the known methods may conduct reaction while supplying nitrogen gas through the atmosphere of reaction system, none of them determine the oxygen concentration in the aqueous phase of the reaction system.
As the use of the polymerization initiator must be limited to a very small amount with respect to the amount of the monomer in emulsion polymerization in order to produce an ultra high molecular weight polymer, the reaction proceeds at a slow rate, and the emulsion thus produced is likely to have poor stability. These problems greatly impede the industrial-scale use of the known methods.
To mitigate these problems, emulsion polymerization is carried out in some methods by using large amounts of emulsifiers, that is, 10 wt % or greater with respect to the amounts of the monomer. As a result, the thus-obtained emulsion contains a large amount of an emulsifier. Therefore, when it is used in the production or processing of paints, adhesives, fibers, paper or the like, the large emulsifier content may cause reductions of water resistance and durability of these products such as films, thus failing to achieve the characteristics expected of an ultra high molecular weight polymer emulsion.
An object of the present invention is to provide a method of producing an ultra high molecular weight polymer emulsion which achieves an increased reaction rate and increased stability of the produced ultra high molecular weight polymer emulsion despite using a limited amount of a polymerization initiator and, further, achieves substantially high water resistance and durability of the processed products of the ultra high molecular weight polymer emulsion, such as films, by limiting the use of an emulsifier to small amounts.